The present invention relates to an internet protocol (IP) network coupling method, a translator for IP networks, and a network system using the translator which are intended to couple a first class IP network in which a plurality of devices of interest are assigned IP addresses of a first class so as to prevent the assignment of the same IP address to different devices and a second class IP network in which a plurality of devices of interest are assigned IP addresses of a second class so as to prevent the assignment of the same IP address to different devices.
The protocol most widely known at present as a protocol for network layers used in the TCP/IP communication is the internet protocol (IP). The IP functions to provide an addressing service for specifying a destination to be communicated with among a large number of nodes connected to a network, and so on, which are the same services provided by the third layer of OSI (Open Systems Interconnection) reference model. Currently, the IP of version 4 (hereinafter called “IPv4”) is commonly used. The IPv4 specification is disclosed in “INTERNET PROTOCOL; DARPA INTERNET PROGRAM PROTOCOL SPECIFICATION”, Information Science Institute University of Southern California, September, 1981. A format defined for a header used in the IPv4 (hereinafter called “IPv4 header”) is as shown in FIG. 11B.
In the IPv4 header, a “version” field stores the version number, i.e., “4”. A “header length” field stores the length of the IPv4 header itself. A “service type” field stores information indicative of a service quality of communication processing. A “packet length” field stores the size of an entire packet which includes a data block treated by the IP and the IPv4 header. Information directed down from an upper layer is treated as a single data block in the IP, and the data block is appended with an IPv4 header in the IP and then sent to a lower layer. Conversely, an IPv4 header included in a packet sent from a lower layer is analyzed by the IP, and a data portion of the packet is sent up to an upper layer depending on the analysis results. An “identifier” field stores an identifier used as reference information when data is passed to an upper layer. A “flag” field stores control information associated with fragmentation of a packet. A “fragment offset” field stores information indicating where fragmented data (fragment) has been positioned in original data. A “time to live” field stores a time during which an associated packet is allowed to exist in a network. A “protocol” field stores information indicating which protocol an upper layer employs. A “header checksum” field stores a checksum for the IP header. A “source IP address” field stores the IP address of a source. A “destination IP address” field stores the IP address of a destination. The IP addresses are assigned to respective nodes connected to a network, and are set respectively to unique values in the network.
While the IP having the specification as mentioned above is currently spreading rapidly over a variety of communication services together with the increasing popularization of the internet, the IP is confronted with a grave problem of exhausted IP addresses.
As countermeasures for solving this problem, the IP of version 6 (hereinafter called “IPv6”) has been proposed at present. The IPv6 specification is disclosed in S. Deering “INTERNET PROTOCOL: Version 6 (IPv6)”, Xerox, PARC, December 1981.
A format defined for a header used in the IPv6 (hereinafter called “IPv6 header”) is as shown in FIG. 11A. In the IPv6 header, a “version” field stores the version number, i.e., “6”. A “priority” field stores the priority of processing executed by a router in a network for relaying a packet. A “flow label” field is used to store an identifier for performing a priority control or the like. A “payload length” field stores the length of a data portion calculated by subtracting an IPv6 header portion from a packet. A “next header identifier” field stores an identifier for identifying which header of upper layer protocol, or which IPv6 extended header follows the IPv6 header. A “hop limit” field stores a maximum number of times of transfers for an associated packet. A “source IP address” field stores the IP address of a source, and a “destination IP address” field stores the IP address of a destination. Additionally, in the IPv6 header, the “source IP address” field and the “destination IP address” field are respectively extended from 32 bits to 128 bits. The extended address fields enable an increased number of nodes to be connected to a network.